ICT1 knockdown inhibits breast cancer cell growth via induction of cell cycle arrest and apoptosis

Failure to Guard: Mitochondrial Protein Quality Control in Cancer

Mitochondria are energetic and dynamic organelles with a crucial role in bioenergetics, metabolism, and signaling. Mitochondrial proteins, encoded by both nuclear and mitochondrial DNA, must be properly regulated to ensure proteostasis. Mitochondrial protein quality control (MPQC) serves as a critical surveillance system, employing different pathways and regulators as cellular guardians to ensure mitochondrial protein quality and quantity. In this review, we describe key pathways and players in MPQC, such as mitochondrial protein translocation-associated degradation, mitochondrial stress responses, chaperones, and proteases, and how they work together to safeguard mitochondrial health and integrity. Deregulated MPQC leads to proteotoxicity and dysfunctional mitochondria, which contributes to numerous human diseases, including cancer. We discuss how alterations in MPQC components are linked to tumorigenesis, whether they act as drivers, suppressors, or both. Finally, we summarize recent advances that seek to target these alterations for the development of anti-cancer drugs.

Functional Diversity of Mitochondrial Peptidyl-tRNA Hydrolase ICT1 in Human Cells

Mitochondria are energy producing organelles of the eukaryotic cell, involved in the synthesis of key metabolites, calcium homeostasis and apoptosis. Protein biosynthesis in these organelles is a relic of its endosymbiotic origin. While mitochondrial translational factors have homologues among prokaryotes, they possess a number of unique traits. Remarkably as many as four mammalian mitochondrial proteins possess a clear similarity with translation termination factors. The review focuses on the ICT1, which combines several functions. It is a non-canonical termination factor for protein biosynthesis, a rescue factor for stalled mitochondrial ribosomes, a structural protein and a regulator of proliferation, cell cycle, and apoptosis. Such a diversity of roles demonstrates the high functionality of mitochondrial translation associated proteins and their relationship with numerous processes occurring in a living cell.

Expression analysis of mammalian mitochondrial ribosomal protein genes

Mitochondrial ribosomal proteins (MRPs) are essential components for the structural and functional integrity of the mitoribosome complex. Throughout evolution, the mammalian mitoribosome has acquired new Mrp genes to compensate for loss of ribosomal RNA. More than 80 MRPs have been identified in mammals. Here we document expression pattern of 79 Mrp genes during mouse development and adult tissues and find that these genes are consistently expressed throughout early embryogenesis with little stage or tissue specificity. Further investigation of the amino acid sequence reveals that this group of proteins has little to no protein similarity. Recent work has shown that the majority of Mrp genes are essential resulting in early embryonic lethality, suggesting no functional redundancy among the group. Taken together, these results indicate that the Mrp genes are not a gene family descended from a single ancestral gene, and that each MRP has unique and essential role in the mitoribosome complex. The lack of functional redundancy is surprising given the importance of the mitoribosome for cellular and organismal viability. Further, these data suggest that genomic variants in Mrp genes may be causative for early pregnancy loss and should be evaluated as clinically.

microRNA-Dependent Modulation of Genes Contributes to ESR1's Effect on ERα Positive Breast Cancer

Background: Dysregulation of ESR1 accounts for endocrine therapy resistance and metastasis of ERα positive breast cancer. However, the underlying molecular mechanism of ESR1 in ERα positive breast cancer remains insufficiency. Notably, to date, a comprehensive miRNA-mRNA regulatory network involved in modulation of ESR1 in development and progression of ERα positive breast cancer is still not established. Methods: Microarray miRNA and mRNA expression profiling from GEO database were used to obtained significant DE-miRNAs and DE-mRNAs in ERα positive breast cancer. Functional enrichment analysis was conducted by Enrichr database. STRING database was utilized to construct protein-protein interaction network, after which hub genes were identified through Cytoscape. Kaplan-Meier plotter was introduced to perform survival analysis. The relationship between ESR1-miRNA or miRNA-target gene pairs were experimentally validated. Results: 74 DE-miRNAs, including 19 upregulated and 55 downregulated miRNAs, and 830 DE-mRNAs, including 359 upregulated and 471 downregulated mRNAs, in ERα positive breast cancer were identified. Potential DE-mRNAs were statistically enriched in several cancer-associated pathways, such as cell cycle and pathway in cancer. Fifty-one hub genes with node degree more than 10 were screened. Twenty-seven of 51 hub genes had significant prognostic values in ERα positive breast cancer. Based on the 27 hub genes, a miRNA-hub gene network, containing 26 miRNAs, was established. Seven of 26 miRNAs were found to possess prognostic predictive roles for patients with ERα positive breast cancer by combination of TCGA and METABRIC data. Intriguingly, ESR1 positively correlated and regulated the 7 miRNAs and the 7 miRNAs inversely correlated and modulated their corresponding downstream targets in MCF-7 and T47D cells, supporting the accuracy of in silico analysis. The relationship between ESR1-miRNA, miRNA-mRNA, or ESR1-mRNA pairs was validated in clinical ERα positive breast cancer. Conclusions: In total, the current findings from this work add substantially to the understanding of ESR1's molecular regulatory mechanism in ERα positive breast cancer.

MiR-1301-3p inhibits human breast cancer cell proliferation by regulating cell cycle progression and apoptosis through directly targeting ICT1

BACKGROUND

MiRNAs regulate a variety of biological processes, such as cell proliferation and apoptosis and play critical roles in cancer progression. Accumulating studies have demonstrated that miR-1301-3p could regulate the development and progression of multiple cancers, but its biological behaviors in breast cancer (BC) are still elusive.

METHODS

The expression of miR-1301-3p was determined in BC tissues and cell lines using quantitative real-time PCR analysis. The effects of miR-1301-3p on BC cell growth, proliferation, cell cycle distribution, and apoptosis were also explored in vitro using MTT, colony formation and Flow cytometry assays. The potential target gene of miR-1301-3p was determined by dual-luciferase reporter assay and verified by quantitative real-time PCR and western blot analysis.

RESULTS

We found the expression of miR-1301-3p was observably significantly down-regulated in BC tissues and cell lines. MiR-1301-3p expression in BC tissues was significantly associated with tumor size and clinical stage. Gain-of-function assays demonstrated that miR-1301-3p inhibited the cell growth and proliferation in breast cancer cell lines, MCF-7 and T-47D. Moreover, up-regulation of miR-1301-3p induced cell cycle G0/G1 phase arrest and apoptosis. Mechanistically, up-regulation of miR-1301-3p reduced the expression of CDK4, Cyclin D1, Bcl-2, but elevated the expression of p21, Bad and Bax. ICT1 was confirmed as a direct target of miR-1301-3p. Furthermore, ICT1 overexpression could partially reverse the effects of miR-1301-3p on BC cell proliferation, cell cycle progression and apoptosis.

CONCLUSION

Our observations suggested that miR-1301-3p inhibits cell proliferation via inducing cell cycle arrest and apoptosis through targeting ICT1, and might be a therapeutic target for BC.

miR-205 regulation of ICT1 has an oncogenic potential via promoting the migration and invasion of gastric cancer cells

Immature colon carcinoma transcript-1 (ICT1) is a newly identified oncogene, which regulates mobility, apoptosis, cell cycle progression and proliferation of cancer cells. Nevertheless, the role of ICT1 and its clinical significance in gastric cancer (GC) is largely uncovered. Here, we found that ICT1 displayed higher expression in GC tissues compared to corresponding tumor-adjacent tissues. Further investigation confirmed ICT1 overexpression in GC cell lines. Clinical data disclosed that high ICT1 expression correlated with distant metastasis and advanced tumor-node-metastasis (TNM) stage. The Cancer Genome Atlas (TCGA) data further demonstrated that GC tissues with metastasis showed a significant higher level of ICT1 compared to those without metastasis. Furthermore, ICT1 overexpression notably predicted poor prognosis of GC patients. Functionally, we demonstrated that ICT1 knockdown suppressed invasion and migration of MGC-803 and BGC-823 cells in vitro. ICT1 overexpression promoted the mobility of SGC-7901 cells. Mechanistically, microRNA-205 (miR-205) was recognized as a direct down-regulator and inversely modulated ICT1 abundance in GC cells. miR-205 expression was down-regulated and negatively associated with ICT1 level in GC tissues. Underexpression of miR-205 indicated an obvious shorter survival of GC patients. miR-205 overexpression inhibited migration and invasion of MGC-803 cells, while these inhibitory effects were reversed by ICT1 restoration. Taken together, we have the earliest evidence that miR-205 regulation of ICT1 functions as an oncogene and prognostic biomarker in GC.